A frequency of a carrier in a high frequency radio apparatus often varies depending on an ambient temperature, individual deviations of components, secular changes, and the like. As a method of detecting a degree of deviation of a frequency of a received carrier from a frequency of an own carrier in such cases, there is conventionally known a method of detecting a phase change point by counting a frequency component of a reception IF (IF stands for an intermediate frequency signal, the same applies to the following description) from a radio part including an antenna using a high-speed clock. In addition, there is also known a method of calculating a frequency deviation amount by performing delay detection on a received carrier and performing a geometric process of a complex baseband signal after the delay detection.
With the former method, an extremely-high-speed count clock is required in order to detect the phase change point of the reception IF. Therefore, current consumption of an entire communication system inevitably increases.
In the case of the latter method, a detection range of the frequency deviation amount is extremely narrow, which leads to a necessity for a local oscillator whose frequency accuracy is extremely high. In other words, the frequency deviation amount obtained from the geometric process of the complex baseband signal is limited to a range of ½ of an absolute value of a symbol rate even by a BPSK modulation/demodulation method necessarily capable of detecting a wide range of a frequency deviation amount. Therefore, as the number of values processed by the modulation/demodulation method increases as in the case of QPSK or QAM, the detection range is significantly narrowed and in the case of a low transmission rate system, higher local oscillation frequency accuracy is required. Consequently, when spread spectrum communication using very weak power is performed, it is impossible to adopt the conventional techniques.
There is also a method of adjusting a local oscillation frequency by setting correction data in a frequency synthesizer. However, such a method requires use of an expensive frequency synthesizer, which hinders miniaturization of a high frequency radio apparatus and also incurs an increase in cost of the entire communication system.
An object of the present invention is to provide a communication method by which it is possible to cope with a frequency deviation of a received carrier, which has been the conventional problem in a high frequency ratio apparatus, at low cost and to readily realize spread spectrum communication that excels in communication quality even with very weak power that is not a subject of regulation by law at low cost, and a high frequency radio apparatus that is suited for implementation of the method.